The present intention relates to a centrifugal extractor in which a cavity for housing a neutron absorption body is provided in the center of a rotor. The centrifugal extractor is used, for example, in reprocessing spent nuclear fuel, to extract and separate U (uranium) and Pu (plutonium).
There is a Purex process which is one of the reprocessing processes for spent nuclear fuel produced from nuclear facilities. This process comprises, as is well-known dissolving the spent nuclear fuel into nitric acid, and separating and recovering U and Pu dissolved in the acid aqueous solution of nitric acid by a solvent extraction operation.
There are some kinds of apparatuses for carrying out the solvent extraction operation, one of which is a centrifugal extractor for carrying out separation of two phases (an aqueous phase and an organic phase) by centrifugal force. The centrifugal extractor is designed so that a rotor is rotatably supported such that the rotor is suspended in a housing, an aqueous phase and an organic phase are supplied to the outer circumference of the rotor and mixed between the housing and the rotor, the mixed phase is sucked into the rotor and separated into two phases in a centrifugal force field generated in the rotor, and the separated phases are discharged to corresponding collectors, respectively (See, for example, U.S. Pat. No. 5,254,075.)
Such a centrifugal extractor as described above has advantages in that processing speed is high, the start-up of the apparatus is quick, the operating efficiency is enhanced and equipment can be simplified, the apparatus can be designed to be smaller, and solvent degradation by radiation can be reduced, as compared with other extractors (for example, such as a mixer-settler extraction apparatus, a pulse column extraction apparatus, etc.). Therefore, the centrifugal extractor is considered to be advantageous for reprocessing a spent nuclear fuel of high burnup and high Pu enrichment produced from a fast breeder reactor, and research and development thereof have progressed.
Considering the shift from the stage of research and development to the stage of practical plant employment, it is necessary to make a centrifugal extractor larger in size and larger in capacity in order to improve the processing ability. However, when an attempt is made to design a large-sized centrifugal extractor using the above-described prior art design technique, criticality control is hard to carry out merely by geometric control, and some countermeasures are necessary in terms of criticality safety. Therefore, it is considered that for example, criticality control is carried out by concentration control or the like, but a process thereof requires complicated and trouble some operation control and poses many problems in terms of safety.
Further, when the centrifugal extractor is made larger in size, the weight and outside diameter of the rotor also increase, and the burden of a supporting means in the upper portion of the rotor becomes great, thus posing a problem that durability of a driving means lowers.
An object of the present invention is therefore to provide a centrifugal extractor in which for larger sizes and larger capacities, enhancement of criticality safety can be achieved.
A further object of the present invention is to provide a centrifugal extractor in which for larger sizes and larger capacities, enhancement of durability can also be achieved.
According to the present invention, there is provided a centrifugal extractor comprising a housing having a bearing disposed thereon, a rotary shaft supported by the bearing and extending downward into the housing, and a rotor rotatably supported in the housing such that the rotor is suspended by the rotary shaft. The rotor is spaced from an inner wall of the housing to form a gap therebetween, and an aqueous phase and an organic phase are supplied to the gap and mixed in the gap. A mixed phase is sucked into the rotor and separated into two phases in a centrifugal force field generated in the rotor, and the separated phases are discharged to corresponding collectors, respectively. A cavity portion is provided in the center of the rotor, and a neutron absorption body is disposed in the cavity portion.
In this case, it is preferable to employ a construction in which the neutron absorption body comprises a cylindrical body standing upright from the bottom of the housing toward the cavity portion in the center of the rotor, and a neutron absorption material sealed into the cylindrical body.
It is also possible to employ a construction in which the neutron absorption body comprises a cylindrical body suspended down from the rotary shaft towards the cavity portion in the center of the rotor, and a neutron absorption material sealed into the cylindrical body.
According to the present invention, there is also provided a centrifugal extractor comprising: a housing having a bearing disposed thereon, a rotary shaft supported by the bearing and extending downward into the housing, and a rotor rotatably supported in the housing such that the rotor is suspended by the rotary shaft. The rotor is spaced from an inner wall of the housing to form a gap therebetween, and an aqueous phase and an organic phase are supplied to the gap and mixed in the gap. A mixed phase is sucked into the rotor and separated into two phases in a centrifugal force field generated in the rotor, and the separated phases are discharged to corresponding collectors, respectively. A cavity portion is provided in the center of the rotor, a cylindrical body stands upright form the bottom of the housing towards the cavity portion, a lower supporting and rotating mechanism of the rotary shaft is disposed at the upper end of the cylindrical body, and a neutron absorption material is sealed into the cylindrical body.